The issue isn't how much current is drawn through one outlet, but how much
current flows through the breaker feeding that outlet.

Two points...

The computer's 750W supply is rated at its maximum capacity. Unless you have
a high-end graphics card and are overclocking the system, it's unlikely
you're pulling 750W. Get a cheap power meter and see what the actual draw
is.

You should absolutely /not/ have a computer system and a high-powered HT
system on the same circuit breaker! Bad idea. If you can't power either one
off its own breaker, you should probably pay an electrician, to set up an
additional line with its own breaker. When my condo was built, I had a
separate breaker installed for the rear power amplifiers.